This project deals with the biosynthesis, localization, and regulation of avian RNA tumor virus proteins in infected cells. Immunoprecipitation, using specific antisera prepared against virion proteins, will be used to isolate viral-specific components from the vast background of host cell proteins. Analysis will involve polyacrylamide gel electrophoresis and tryptic peptide mapping. Previous research by the principal investigator has demonstrated that the major internal structural proteins of avian oncornaviruses are generated by proteolytic cleavage of a large precursor polypeptide. Cell fractionation techniques will be used to study the site of synthesis as well as the nature of the interaction of this precursor, and other virion components, with the host cell. In order to gain further insight into how the processing of viral proteins could act as a locus of control, these studies will be extended to include several systems where virus formation has been shown to be restricted or aberrent, such as in avian oncornavirus transformed mammalian cells and the replication of certain genetically recombinant viruses.